A goal early in the first half from Pierre-Emerick Aubameyang sealed the win for Thomas Tuchel's side and brought an end to Bayern's unbeaten start to their league title defence.

The result leaves the Bavarians with 24 points from their first 11 matches, marking their worst start to a season since they posted just 16 points in the same period under Louis van Gaal in 2010-11.

And Lahm says their defeat underlines the fact that the German top flight is far tougher than Bayern made it appear to be during their dominance under Jupp Heynckes and Pep Guardiola in the last four seasons.

"Our game wasn't bad, just okay," he said. "Unfortunately we conceded the early goal and then we missed that final pass. Otherwise we would have been able to create a lot of chances.

"I said many times in recent years, but nobody wanted to believe me: it's not this easy to be on the top of the table all the time and to confirm these achievements. It's a difficult task - now we'll see just how difficult."

Bundesliga newcomers RB Leipzig are three points clear at the top after their 3-2 victory away to Bayer Leverkusen, ending a run of 39 matchdays in which Bayern have topped the table.

Lahm admits it is difficult to say for how long the leaders can sustain their form.

Asked if they could seal a shock title win, he said: "I don't know, I'm not clairvoyant. For now, they are doing really well. They won in Leverkusen, which is never easy. We have to wait and see how long momentum is on their side."

Goalkeeper Manuel Neuer feels Bayern have been made to pay for dropped points against Cologne, Eintracht Frankfurt and Hoffenheim as much as against Dortmund.

"Before the game, I didn't look at the table, but now we should do that," he said. "It's extremely annoying - not only because of this game but because of the draws. We gave away the points."